The present invention relates to the use of catheters in performing infrared imaging to inspect and characterize the lumen of a blood vessel, especially a coronary artery.
Visual imaging of internal body structures has heretofore been performed in certain medical procedures. For example, visual imaging by means of endoscopes introduced into the body has been useful in guiding the movements of certain medical devices inserted into the body for body treatment, and to view the results.
It is necessary that the body region in which the visual imaging, or endoscopy, is to be performed, contain a fluid that is transparent to the light wavelengths being utilized. Thus, visual imaging within body cavities such as the stomach can be performed after evacuating the stomach.
A form of endoscopy, called angioscopy, has been performed in coronary arteries. However, substances in the blood can obscure the image. For example, light can be scattered by red blood cells and absorbed by hemoglobin in the blood. Accordingly, it has been required that blood first be removed from the arterial region being inspected, and replaced with a clear saline solution which is transparent to the light wavelength. Difficulties such as this in obtaining a clear image have limited the usefulness of visual imaging of blood vessels.
The imaging of internal body cavities has also been performed by sensing infrared radiation emitted from body structures (see U.S. Pat. Nos. 5,445,157 and 6,178,346). In U.S. Pat. No. 6,178,346 for example, it has been proposed to inspect the lumen of a coronary artery by introducing into the artery a catheter which emits infrared light toward the wall of the lumen. Light that is reflected from the lumen wall is directed to an infrared camera so that a real-time image of the lumen wall can be formed. Such a procedure enables physicians to identify potentially dangerous plaque build-up and lesions on the lumen wall, and specifically identify characteristics of vulnerable plaque in the lumen wall intima.
It would be desirable to provide improved methods and apparatus for imaging a lumen of a blood vessel, such as a coronary artery using light of any suitable wavelength, intensity and duration, chosen independently of the light-absorption and light-scattering characteristics of blood.
It would also be desirable to provide such methods and apparatus which can utilize relatively low intensity light in the near infrared region, especially 0.8 to 1.4 microns.